1. Field of the Invention
The present invention relates to a system for modifying properties of an article of footwear. The invention concerns, more particularly, articles of footwear having a foot-supporting member with replaceable inserts.
2. Background of the Invention
Modern articles of athletic footwear are generally fitted to specific individuals based solely upon the overall length of the foot. Foot dimensions, however, vary between individuals in respects that are not accounted for through consideration of length alone. As a result, many individuals may select footwear that is improperly-fitted and has the potential to cause discomfort or impair athletic performance.
The fit of an article of footwear is primarily influenced by the shape of the last upon which the footwear is formed. In creating a last, primary importance is given to foot measurements that include the overall length of the foot, width of the foot, height of the first digit, contour of the instep, and at least six girth measurements. In shaping a last for the manufacture of mass-produced footwear, designers utilize foot measurements from a broad spectrum of the population to determine the characteristics of a statistically-average foot. The measurements that comprise the statistically-average foot are then used to shape a last that theoretically achieves a proper fit for a majority of the population. Many individuals, however, do not have a foot with statistically-average proportions and would obtain benefits from footwear that accommodates their unique proportions. For the majority of these individuals, footwear that is offered in a variety of length-width combinations would provide a sufficient fit. Most footwear manufacturers, including manufacturers of athletic footwear, only provide consumers with footwear in limited length-width combinations. For a given length, therefore, most footwear manufacturers provide consumers with few options, if any, for different widths.
The primary factors that effectively prohibit manufacturers from offering footwear sizes in a variety of widths for each length relate to manufacturing costs and retail inventory. Each length-width combination for an article of footwear generally requires a unique last that is proportioned for the specific length-width combination. In addition to the cost of generating a relatively large number of lasts, further expenditures are required to alter the manufacturing system each time a different length-width combination is manufactured. The most expensive aspect, however, may be generating molds for midsole-outsole units that reflect a variety of length-width combinations for both the left and right foot. Such costs are generally reflected in the final price of the footwear and may make the footwear prohibitively expensive when compared to the cost of similar footwear that is not offered in a variety of widths. With regard to retail inventory, the cost of acquiring footwear in multiple length-width combinations and storing the inventory until sale effectively prohibits at least the smaller retailers from offering various length-width combinations. To ensure availability of specific sizes of footwear, retailers often purchase numerous pairs of footwear for each size that is based on length. When the typical inventory requirements are further multiplied by numerous widths, the size of the required inventory becomes increasingly large. Accordingly, both manufacturing costs and limitations upon retail inventory effectively prohibit manufacturers from offering a variety of widths for each size.
Providing footwear with a variety of length-width combinations may not provide a sufficient fit for individuals with foot proportions that change in relatively short periods of time. Children, for example may experience rapid growth changes that prevent footwear from being worn for a significant portion of the footwear's useful life. Individuals with specific medical conditions, such as edema, may also experience changes in foot proportions. In addition, changes in foot proportions may occur during maternity.
In order to accommodate individuals that do not have feet with statistically-average proportions or proportions that change over time, some prior art footwear designs incorporate fit features that are adjustable. The prior art designs exhibit both automatic and manual mechanisms that permit adjustment of fit factors. An automatic mechanism adjusts by utilizing the pressure of the foot against the interior of the shoe. Usually adjusting for width, the typical automatic mechanism permits a vertical deformation of the upper to translate into a horizontal increase in width. Examples of patents displaying automatic mechanisms include U.S. Pat. Nos. 5,404,658 to Rosen; U.S. Pat No. 5,325,614 to Rosen; U.S. Pat. No. 5,241,762 to Rosen; U.S. Pat. No. 5,060,402 to Rosen; U.S. Pat. No. 4,967,492 to Rosen; and U.S. Pat. No. 4,858,340 to Pasternak. Manual mechanisms require the wearer to adjust fit through means that include lacing systems, as in U.S. Pat. No. 4,553,342 to Derderian et al. And U.S. Pat. No. 641,642 to Gunn, or screw adjustments, as in U.S. Pat. No. 4,391,048 to Lutz; U.S. Pat. No. 3,686,777 to Rosen;  U.S. Pat. No. 2,607,133 to Marlowe; and U.S. Pat. No. 5,729,912 to Gutkowski et al.
Although the prior art succeeds in supplying means for adjusting fit factors, most of the prior art designs are not suitable for athletic footwear. The automatic mechanisms rely solely on the pressure of the foot against the interior of the shoe to adjust fit. The high pressure exerted by many modern sports would make this style of shoe unstable. Furthermore, the manual adjustments often require mechanical devices within the sole that are difficult to adjust competently and add weight to the shoe. The present invention provides a system for modifying the properties of an article of footwear, including the fit of an article of footwear.